EVOLVING NATM FOR SANTIAGO'S METRO

This is the first of a two-part series on the construction of the Metro de Santiago, which started with open cut stations and running tunnels and has progressed to totally underground construction in mined tunnels and caverns. These excavations represent some of the most advanced NATM (New Austrian Tunneling Method) design and excavation underway in the world today. The new mining process helps avoid conflicts with Santiago's traffic, is cost-effective, and promises to be more so with the introduction of advanced value engineering. Construction methods have evolved rapidly, starting in the mid-70s with an operating system based on rubber-tired rolling stock. With more than half of the 43-km network underground objections to cut and cover construction were mounting, which led to the policy of less intrusive methods starting in the late 80s. Underground conditions are near perfect. Ground water levels are far below the depth needed for the Metro, and the soil is stable with high rigidity. By using mine techniques instead of open boxes, the project cut costs by 60% from one 3 km line extension to a more recent one.